An investigation of the variables affecting pullout of seven-wire prestressing strand

The pullout strength of untensioned prestressing strand is a function of several variables. This study is an attempt to identify and isolate these variables. Reviews of the existing studies of pretensioned and untensioned strand as well as the pullout testing of larger size untensioned strands are included. The influence of strand diameter, concrete strength, length of embedment, and surface condition of the seven-wire strand was investigated. Relationships were developed between steel stress at the time of slippage and embedment length of strand for a given surface condition. These relationships were compared with recommended equations from previous work. The data was normalized by bond stress and some dependence of concrete compressive strength is suggested. The major contributing factors affecting the pullout capacity of seven-wire prestressing strand were found to be the length of embedment and the surface condition of the strand.